Community Education on Environment and Development

Watering and Mulching Vegetable Gardens


Among the most common mistakes made by gardeners is incorrect watering. A great number of plant problems are directly or indirectly a result of incorrect watering. In Western Washington, the biggest problem is under watering. Many people assume that we are in a rainy climate and watering is unnecessary or that a light sprinkling will do in dry times. Both of these attitudes are dead wrong. During dry periods common to Seattle summers, plants need water and watering must be done thoroughly – a light sprinkling does not help. Plants absorb water through their roots, so enough water must be applied to soak the soil to several inches deep where the roots are.

The only way to figure out when and how much to water is to stick your hand into the soil (or use a shovel if the soil is too hard) and see/feel where the moisture level is. Based on this test you can determine when water is needed and how much to apply.

Soil should never be wet on the surface and dry an inch or two down. Check the soil just after watering and several hours (or the next day) after watering to see how fast the water seeps to what depth in the soil. Take this seepage into account for future watering.

Seeds and seedlings need moisture closer to the surface then mature plants, so they need more frequent watering. Once plants are established, less frequent, deep watering with dry periods between helps grow deep roots. Plants encouraged to root deeply are more drought tolerant and require less care than shallow-rooted ones.

Some crops are naturally more deep rooted than others. Generally, leafy crops like lettuce, spinach and mustards are shallow rooted. Soil should never dry out below 2-3 inches down. The same is true for onions and their relatives like leeks, garlic and shallots.

Roots crops, beets, carrots, potatoes, and radishes, should be kept evenly moist (no wet-dry alternatives) or they develop tough zones.

Don’t wait for the plant to wilt! After a few wilts, the plant will be stunted and production will not be as good.

Some Watering Tips


Weed control and watering are two of the biggest jobs once your garden is planted. Both of these jobs can be easier if you use mulch. The two most common kinds of mulch are plastics, and organic material such as straw, leaves, sawdust and wood-chips, clippings or compost.

Black plastic gives total weed control, keeps the soil moist and allows the soil to get warmer as we get more sunny weather. (Don't use clear plastic if you want weed control. Poke holes in the plastic so you can get water through it when you do have to water.

Organic mulches keep the soil moist and cut down on the weeding but keep the sun from warming the soil. For this reason, it is best not to put on organic mulches until the soil has warmed up, usually late June. The really nice thing about organic mulches are that you can spade them under in the fall or winter which helps improve your garden soil.

Keep in mind four cautions:

  1. Don't use grass clippings from lawns that have been recently treated with a herbicide like "Weed and Feed."
  2. Mixing in large amounts of sawdust or straw may "tie up" the nitrogen in your soil so your vegetables get yellow or stunted. Adding nitrogen fertilizer when you dig in the mulch or plant the next crop will prevent this.
  3. Loose organic mulch may provide nice, moist hiding places for slugs, so be prepared to bait for them.
  4. Some kinds of organic mulches, especially hay, may contain lots of weed seeds and make more work than they save. Check hay or straw for seed heads before buying or using.

All in all, mulches are a real labor saver. We've probably all picked dirty strawberries and gritty spinach after a heavy rain. Clean fruits and vegetables are one of the nice fringe benefits of mulching.

Copyright: WSU Coop Extension

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